SažetakA young fit male person was exposed to three laboratory loads, simulating his own professional working conditions. The loads represented cycling at 350, and 650 kpm/min-1, two different climates with ta = 16° C, RH = 80%, v = 0,3 m sec-1, and ta = 30° C, RH = 80%, v = 0,3 m sec-1, and finally the breathing through the respirator »DRAGER with two filters M 105 St«, and breathing without respirator. These loads were combined and each was repeated at random. The subject performed work, each following experimental day, at the same time in 8 cycles, consisting of 15 minutes cycling and 5 minutes rest, and of a half on hour rest at the end of the 8th cycle. The subjective rating of rectal temperature (tR) was recorded. We found different loads significantly correlated with subjective rating of fatigue, which might contribute to the reliability of the method applied at different sources of fatigue. The particular question of the reliability was continued by the repetition of each combination of loads. Between the first and the second application no significant difference existed, whereas the correlation coefficient was 0.75. Subjective rating of fatigue showed a systematic tendency to increase, while the regression line was clearly linear. Likewise the fH was correlated with subjective rating of fatigue; however, to be on safe side, we would say the same factors influenced the increase of fH as that of subjective rating of fatigue. On the other handtR, was in no correlation with subjective rating of fatigue. The results found in one subject could not be generalized without criticism, but for all that we assume that subjective rating of fatigue method could be applied with a satisfactory reliability at various physical loads after the subject has been trained and during work asked sufficiently often.